The present invention relates generally to the deposition of diamond-like coatings on substrates and, more particularly, to the deposition of fluorinated diamond-like coatings on substrates using plasma immersion ion processing.
Diamond-like carbon (DLC) films are known for their high hardness, wear resistance and low friction. Many applications have been developed for these coatings and their modified counterparts. A scratch resistant and extremely hard coating with excellent hydrophobic (un-wetting) properties has numerous practical applications ranging from non-stick kitchenware to protective coatings for optics. Since DLC is itself only mildly hydrophobic, different elements such as F, N, O or Si, have often been incorporated into it by using a variety of techniques (see e.g., M. Grischke et al., Surf. Coat. Technol. 74, 739 (1995)). The fluorination of thin films and surfaces can be achieved using both etching and deposition treatments. However, the fluorine incorporation in surfaces after the widely used C2F4 plasma etching process is only a few nanometers deep (see, e.g., Y. Lin and L. J. Overzet, Appl. Phys. Left. 62, 675 (1993) and C. Vivensang et al., Diamond Relat. Mater. 3, 645 (1994)), thereby limiting the applications of the treated surfaces. The deposition of different types of fluorinated films such as fluoropolymer films by sputtering of polytetrafluoroethylene (PTFE) onto targets or by using plasma-assisted deposition has been well established (see, e.g., D. Fleisch et al., J. Membrane Sci. 73, 163 (1992) and F. Quaranta et al., Appl. Phys. Lett. 63, 10 (1993)). For the plasma deposition of F-DLC films fluorocarbon-hydrocarbon mixtures have been mostly used (see, e.g., D. Fleisch et al., J. Membrane Sci. 73, 163 (1992), R. S. Butter et al., Thin Solid Films, 107 (1997), and J. Seth and S. V. Babu, Thin Solid Films 230, 90 (1993)). The results from various studies by different groups have shown that the un-wetting properties of F-DLC films can reach the performance of PTFE and the hardness and wear resistance have been kept relatively high (see, e.g., M. Grischke et al., Diam. Relet. Mater. 7, 454 (1998) and C. Donnet et al., Surf. Coat. Technol. 94-95, 531 (1997)). Earlier studies have also shown that the contact angle behavior of the F-DLC films produced with plasma techniques from fluorocarbon-hydrocarbon gas mixtures depends on the incorporation of CF2 and CF3 groups rather than CF group (see, e.g., D. Fleisch et al., supra, H. Kasai et al., J. Phys. D19, L225 (1986), and J. Seth and S. V. Babu, supra). This incorporation then depends on the composition of source gases, deposition technique and parameters and plasma chemistry that take place during the deposition.
In order to attain widespread utilization, a method for deposition of thin films must be readily scalable to a production scale. This also applies to F-DLC films. To date, all plasma deposition techniques that have been used to produce hard F-DLC with good un-wetting properties have been line-of-sight processes. Thus, complex-shaped objects are difficult to uniformly coat. Plasma Immersion Ion Processing (PIIP) for the deposition of F-DLC coatings differs from the Plasma Source Ion Implantation (PSII) process by employing a low pulsed-bias voltage, typically less than 10 kV, and enables the deposition of thin films on various substrate materials (see, e.g., K. C. Walter et al., Surf. Coat Technol. 93, 287 (1997) and S. M. Malik et al., J. Vac. Sci. Technol. A15, 2875 (1997)). Additionally, PIIP enables conformal deposition over large areas (see, e.g., J. R. Conrad et al., J. Appl. Phys. 62, 4591 (1987)).
Accordingly, it is an object of the present invention to provide a method for depositing fluorinated, diamond-like coatings on chosen substrates using a non-line-of-sight process.
Another object of the present invention is to provide a method for depositing fluorinated, diamond-like coatings on chosen substrates using plasma immersion ion processing.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the method for depositing a fluorinated, diamond-like carbon coating on a selected substrates includes the steps of: applying a negative-pulsed bias to the substrate, and immersing the biased substrate in a plasma containing ions simultaneously bearing carbon and hydrogen and carbon and fluorine, whereby the ions are projected onto the surface of said substrate and form a fluorinated, diamond-like coating on the surface thereof.
Preferably, the plasma is formed in a gas mixture including acetylene and hexafluoroethane.
It is also preferred that the substrate includes silicon.
Benefits and advantages of the present invention include conformal deposition of fluorinated, diamond-like carbon coatings over large areas.